Our taste for meat has also led us into some troubleour teeth are too big for our downsized jaws and most of us need dental work.

"It's really amazing what we know now that we didn't know 15 or 20 years ago," said Mark Teaford, a professor at Baltimore's Johns Hopkins University. Teaford helped organize a panel discussion on human diet from a number of perspectives:

 How did the ability to eat meat shape the evolution of humans?  What can we learn about early humans from tooth shape?

Carnivorous humans go back a long way. Stone tools for butchering meat, and animal bones with corresponding cut marks on them, first appear in the fossil record about 2.5 million years ago.

How Did Meat-Eating Start?

Some early humans may have started eating meat as a way to survive within their own ecological niche.

Competition from other species may be a key element of natural selection that has molded anatomy and behavior, according to Craig B. Stanford, an ecologist at the University of Southern California (USC).

Stanford has spent years visiting the Bwindi Impenetrable Forest National Park in Uganda, Africa, studying the relationship between mountain gorillas and chimpanzees.

"It's the only forest where mountain gorillas and chimps both live," he said. "We're trying to understand the ecological relationshipdo they compete for food, for nesting sites?"

The key difference between chimps and gorillas ecologically is that chimps eat meat and gorillas don't. A total herbivore is able to coexist with an omnivore because they have significantly different diets.